The invention relates to electrical stepping motors and more particularly to such stepping motors that are connected to drive a transducer carriage in a magnetic disk file machine.
Stepping motors have previously been proposed for driving the transducer carriages in disk drive machines. A series of stator coils are sequentially energized in order to cause the rotor of the stepping motor to move between initial and target positions with corresponding movements of the transducer carriage between corresponding initial and target positions. The final stator coil is energized in order to hold the rotor of the motor and the transducer carriage in target positions; however, a substantial length of time is required thereafter for the rotor of the motor and the carriage to actually stop in target positions due to the rotor and carriage ringing or oscillating about their target positions. This is particularly true when certain mechanical connections are used between the motor rotor and the carriage forming a simple spring-mass system that allows oscillations of the rotor with respect to the carriage and increases the time required for the carriage and motor rotor to actually stop. Such a transducer carriage is commonly slidably disposed on guide rods which allow the carriage to move across the associated magnetic disk with corresponding movement of a transducer carried by the carriage, and it has been proposed that the friction between the carriage and its supporting guiderods be increased in order to reduce the ringing or oscillation of the transducer carriage in the vicinity of its target position. Such increased guide rod friction, however, although causing the carriage to stop in a reduced time, decreases the accuracy with which the transducer carriage may be located with respect to target position.